This research is the result of the interaction of geneticists, embryologists, molecular biologists, cell biologists, immunologists and virologists of The Wistar Institute in studies of the relationship between cell differentiation and cancer and of the regulation of gene expression in stem versus differentiated cells. A variety of experimental approaches and cellular systems is used by the different investigators to probe erythroid, myeloid, and lymphoid differentiation and to understand their relation to cancers of the hematopoietic system. The role of the translocation of the c-abl and c-sis oncogenes in CML has been evaluated.